so ive been putting off doing a proper mobile install for like two years now and finally bit the bullet last weekend. got the FT-857D mounted under the passenger seat on a RAM mount bracket thing, ran the power cables directly to the battery with an inline fuse, and put up a Tram 1185 on the roof with a mag mount for now until i can figure out the NMO situation on my tacoma.

everything works great on HF mostly, but on 2m and 70cm im getting this weird buzzing/whining noise that changes pitch with the engine RPM. classic alternator whine i think? but i already used pretty heavy gauge wire direct to battery so i thought that would fix it. the noise isnt horrible but its definitely there and i know people on the other end can hear it too because my buddy told me my audio sounds rough when im driving.

not sure if its a grounding issue or if i need one of those ferrite chokes on the mic cable or maybe a noise filter on the power line. anyone dealt with this before? im not totally new to radio but mobile installs are kind of new territory for me

the whine changing with RPM is almost always alternator noise getting into the audio somehow. a few things to check — first make sure your radio chassis is grounded to the vehicle chassis with a short heavy wire, not just relying on the power cable ground back to the battery. sometimes that alone fixes it. second, try wrapping your mic cable a few times through a ferrite toroid right at the radio end, that can kill a lot of RFI pickup on the cable itself.

also check if the noise is on receive or just transmit, or both. if its mostly on transmit its often the mic line picking something up. if its on receive too then youve got RF or noise getting into the front end somehow, maybe antenna cable routing too close to something noisy under the hood or in the cab. the mag mount being temporary might also mean the ground plane isnt great which can cause all kinds of weirdness on VHF/UHF. a proper NMO through the roof will almost certainly improve things a bunch once you get there.

yeah i had the exact same problem when i put my 7100 in my jeep, drove me crazy for weeks. ended up being that i hadnt grounded the radio body to the frame, just had the negative going back to battery and thought that was enough but it wasnt. added a short piece of 10 gauge from the radio chassis to the nearest bolt on the body and the whine dropped like 90 percent. still had a little left and a cheap inline noise filter from Amazon on the power leads got rid of the rest. total cost like 8 bucks for the filter lol.